Inkjet printers operate by placing small droplets of ink onto a medium, (e.g., a sheet of paper) to create an image. Inks used in inkjet printers are typically stored in and dispensed from one or more inkjet cartridges that are specific for the inkjet printer with which they are used. Once the ink in the inkjet cartridge has been used, the cartridge must be replaced or refilled. Refilling of inkjet cartridges is a relatively simple task and refill kits are readily available.
The ease with which inkjet cartridges may be refilled lends itself to a high susceptibility for counterfeiting. This can lead, for instance, to damage to the reputation of an ink manufacturer if in an inkjet cartridge is replaced with a counterfeit ink of inferior quality and sold with the manufacturer's label attached to the cartridge. Additionally, counterfeiting may lead to large expenditures of warranty monies paid out by an ink manufacturer if, for example, an authentic ink of the ink manufacturer is replaced with a counterfeit ink, or diluted, and then returned to the manufacturer accompanied by a complaint of substandard ink quality.
Techniques have been developed for tagging various articles to prevent counterfeiting or at least reduce the incidence thereof. For instance, the various articles may be tagged with code-bearing micro-particles, bulk chemical substances, or radioactive substances. However, tagging techniques that are applicable to other articles or materials are not necessarily suitable for tagging inks. Inks are typically formulated to provide maximum performance in terms of, among other traits, color, physical and chemical properties, and interaction of the ink with the medium on which they are printed.
Some identification techniques for tagging and tracing materials such as inks, paintings, explosives, pollutants, and other articles exist. These techniques may employ inorganic salts, ultraviolet (UV) absorbers, nucleic acids or metals as a tag, wherein the tag is used to identify or authenticate the tagged material. Analytical tools used to detect these tags or traces include paper chromatography, UV-visible spectrophotometers, X-ray microanalysis or electrophoresis.
Although these techniques may enable the detection or quantification of the tagged material, the incorporation of the tag into the ink may hinder ink development by the ink manufacturer. For instance, ensuring printer performance is an expensive and time-consuming process for the ink manufacturer and the prevention of counterfeiting inks further frustrates the goal of ensuring printer performance.
While some metal and other multi-valent salts may have utility in tagging certain articles, they are not suitable for tagging inks used in thermal ink-jet printers because trace amounts of unwanted cations such as Fe3+, Cr3+ and Si4+ may cause mis-directed ink drops or mis-firing of the ink jet nozzles. Further, the use of UV absorbent materials or other fluorescent brighteners may add unwanted effects to color appearances of the ink or may fade upon prolonged exposure to light.